telescope

(instrument to observe at a distance)

A telescope is an instrument to observe objects and phenomena at
a distance from the telescope, presenting a magnified image of
the EMR as received from the object itself, gaining
some of the advantages of closer observation. Older/traditional usage
of the term refers to an optical instrument, but with
the development of the ability to detect other EMR bands,
the term is used in a wider sense, often qualified, e.g.,
"radio telescope".

Telescopes are used in and outside astronomy, and within astronomy,
both by the generally-interested and by researchers. Research
telescopes come in all sizes but include the larger units, with
larger diameters, which give them the ability to resolve more detail
and observe fainter (e.g., more distant) objects. The largest
optical telescopes are on the order of 10m in diameter with up to
30m in development (extremely large telescopes). The largest radio telescopes
include 100m diameter units that can be aimed and 300m units with
limited pointing capability.